1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by using a perpendicular magnetic recording system and to a head gimbal assembly, a head arm assembly, and a magnetic disk drive each of which incorporates the magnetic head for perpendicular magnetic recording.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction perpendicular to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be influenced by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
A magnetic head for perpendicular magnetic recording comprises: a medium facing surface that faces toward a recording medium; a coil for generating a magnetic field corresponding to data to be written on the recording medium; and a pole layer allowing a magnetic flux corresponding to the field generated by the coil to pass therethrough, and generating a write magnetic field for writing the data on the recording medium through the use of a perpendicular magnetic recording system. The pole layer incorporates a track width defining portion and a wide portion, for example. The track width defining portion has an end located in the medium facing surface. The wide portion is coupled to the other end of the track width defining portion and has a width greater than the width of the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, it is an improvement in magnetic head and an improvement in recording medium that mainly contributes to a higher recording density. It is a reduction in track width, that is, a reduction in width of the end face of the pole layer located in the medium facing surface, and an improvement in writing performance that is particularly required for the magnetic head to achieve higher recording density. An improvement in writing performance is, for example, an improvement in overwrite property that is a parameter indicating an overwriting capability. The overwrite property deteriorates if the track width is reduced. Therefore, it is required to achieve a better overwrite property with a reduction in track width. To improve the overwrite property, it is effective to use a material having a high saturation flux density as the material of the pole layer.
It is an improvement in writing resolution that is required for the recording medium to achieve higher recording density. It is effective to increase the magnetic coercivity of the recording medium to improve the writing resolution. In this case, too, it is required to use a material having a high saturation flux density as the material of the pole layer so as to obtain a sufficient overwrite property when the recording medium having a great coercivity is used.
Against such a background, since it is impossible to obtain a sufficient saturation flux density through the use of a conventional FeNi alloy such as one having a composition of 18 weight % Fe and 82 weight % Ni or a composition of 50 weight % Fe and 50 weight % Ni, other materials having a high saturation flux density are considered for use as the material of the pole layer. To be specific, high saturation flux density materials such as an FeCo alloy, a CoNiFe alloy, FeC and FeN are considered for use as the material of the pole layer.
In a magnetic head for perpendicular magnetic recording, it is known that there is a phenomenon in which data stored on a recording medium is erased by a magnetic field produced by the pole layer due to residual magnetization of the pole layer when writing operation is not performed, which is hereinafter referred to as “pole erase phenomenon”. It has been found that the pole erase phenomenon is likely to occur if the above-mentioned types of high saturation flux density materials are used as the material of the pole layer.
The likelihood of occurrence of the pole erase phenomenon depends on the shape of the track width defining portion of the pole layer. Japanese Published Patent Application (hereinafter referred to as “JP-A”) 2003-296906 and JP-A 2003-317212 each disclose a technique for suppressing an occurrence of pole erase phenomenon by improving the design of the shape of the track width defining portion.
The likelihood of occurrence of the pole erase phenomenon also depends on the magnetic domain structure of the pole layer. The Journal of the Magnetic Society of Japan, vol. 27, No. 3, pp. 124-128, 2003 discloses a technique for suppressing an occurrence of pole erase phenomenon by reducing the throat height and thereby stabilizing the domain structure of the pole layer.
A variety of techniques have been proposed for stabilizing the domain structure of the pole layer by improving the shape of the pole layer and the structure around the pole layer of a magnetic head for longitudinal magnetic recording, as disclosed in JP-A 2000-331310, JP-A 11-161913 (1999), and JP-A 11-328615 (1999), for example.
JP-A 7-14118 (1995) discloses a technique for stabilizing the domain structure of the pole layer by improving the structure around the pole layer of a magnetic head for perpendicular magnetic recording.
Japanese Examined Patent Application Publication (hereinafter referred to as “JP-B”) 1-7401 (1989) and JP-A 8-241503 (1996) each disclose a technique for controlling the domain structure of the pole layer by controlling the magnetostriction constant of a magnetic material forming the pole layer of a magnetic head for longitudinal magnetic recording. To be specific, JP-B 1-7401 discloses a technique for suppressing magnetic instability by using a NiFe alloy (81 to 84 weight % Ni and 19 to 16 weight % Fe) having a negative magnetostriction constant as a magnetic material forming the pole layer. JP-A 8-241503 discloses a technique for optimizing the magnetic domain structure of the pole layer by using a CoNiFe alloy (65 to 80 weight % Co, 15 to 25 weight % Ni and 8 to 25 weight % Fe) having a positive and great magnetostriction constant as a magnetic material forming the pole layer.
JP-A 60-59509 (1985) discloses a method of forming a thin film having an isotropic magnetic property that is used for a pole layer of a magnetic head for perpendicular magnetic recording. This publication discloses a Permalloy film having a composition of 78 weight % Ni and 22 weight % Fe as a specific example of the thin film.
As described above, each of JP-A 2003-296906 and JP-A 2003-317212 discloses the technique for suppressing an occurrence of pole erase phenomenon by controlling the shape of the track width defining portion. However, the shape of the track width defining portion has a great influence on the characteristics of the magnetic head. Therefore, there is a possibility that the characteristics of the magnetic head could be affected by designing the track width defining portion to have a special sort of shape to suppress an occurrence of pole erase phenomenon.
There is also a possibility that the characteristics of the magnetic head could be affected by modifying the shape of the pole layer or the structure around the pole layer to stabilize the domain structure of the pole layer as proposed in JP-A 2000-331310, JP-A 11-161913, JP-A 11-328615 and JP-A 7-14118.
Furthermore, a saturation flux density as high as one required for the pole layer of a magnetic head for perpendicular magnetic recording cannot be obtained through the use of the materials disclosed in JP-B 1-7401, JP-A 8-241503 and JP-A 60-59509.
Furthermore, it is unknown whether it is possible to suppress an occurrence of pole erase phenomenon through the use of the techniques disclosed in JP-A 11-161913, JP-A 11-328615, JP-A 7-14118, JP-B 1-7401, JP-A 8-241503 and JP-A 60-59509.